1. Field of the Invention
The present invention relates in general to an electrophotographic copying apparatus of a movable copy board type, and more particularly concerns a structure and application of a reflector mirror which serves to direct light rays emitted from an original illuminating lamp upon energization thereof in a predetermined direction.
2. Description of the Prior Art
In the prior art electrophotographic copying apparatus or machine, the reflecting mirror is used only for directing the light ray emitted from the illuminating lamp toward a location on a path along which the copy board is moved and mounted to side frames of the copying machines at an appropriate position in combination with other members or components. The use of the reflector mirror for the other purposes has not been conceived. For mounting the reflector mirror on the machine frame, portions of the frames are bent inwardly with through holes being formed in the bent portions. On the other hand, either through-holes or threaded holes, in the case of which the thickness of the reflector is thick, are formed in the reflector mirror at appropriate locations, whereby the reflector mirror is fixedly secured to the frames through screw connections. Since the frames are usually formed with notches and large holes for mounting various parts thereon, there are necessarily produced in the frames mechanically strong and feeble portions. If the copying machine is assembled without paying any special consideration to the portions of a poor mechanical strength, a parallel arrangement of both frames which have to be disposed with a substantially uniform distance therebetween would be disturbed under unbalanced load, giving rise to a danger that the apparatus could not properly be operated (e.g. a stable running operation of the copy board may not be attained). With a view to evading such difficulties, a large number of supporting members are used for maintaining the structural integrity of the machine frames or alternatively the frames are made of heavy and thick members, which however requires troublesome procedures for assembling the machine frames and hence the copying machine. Of course, the bent portions described above may be utilized for the reinforcing purpose. However, the size of such bent portions provided in the frames of the copying apparatus is considerably small as compared with the dimension of the frames. Thus, the bent portions are not in the position to be used for reinforcement in like manner with the inherent supporting members. Further, the use of heavy or thick members for the frames to accommodate reduced mechanical strength is disadvantageous in that the weight of the whole apparatus is correspondingly increased. With the hitherto known structure of the copying apparatus, there arises in addition to the problems discussed above a difficulty that the positional relationships between the copy board and other members to be mounted on the frame, more particularly the illuminating apparatus, cannot be controlled with a desired accuracy in a facilitated manner. By way of example, a process of determining the mounting positions for various members to be mounted on the frames and machining the latter correspondingly will be described below.
Heretofore, provision of the threaded holes, notches and through-holes in the frames for mounting requisite members thereon has been effected usually in the following manner. In the first place, a flat plate cut in a proper size is positioned on a ruler plate along one side in an upstanding state, wherein a line is ruled at a predetermined portion to be processed or machined with one side in contact with the ruler plate and one of the sides extending perpendicularly to the former being used as a positional reference. Subsequently, the ruled portion is correspondingly machined. Thereafter, the bent portion is formed along the ruled line to install the rails for supporting and guiding the copy board. In the meantime, it is assumed that the positions of the other units such as the drum shaft supporting position, the developing device installing position or the like have been indexed properly. In forming the bent portions, it is very difficult to obtain them as precisely as the ruled line indicates. In reality, the provision of the bent portion is only possible with error which is significantly great as compared with the error involved in the formation of a hole. More particularly, the distance to the provided bent portion from the reference position (i.e. the reference side brought in contact with the ruler plate at the ruling step) will become different from one frame to the other. Further, distances between the paired bent portions will become different when the finished frames are disposed in opposition to each other. Consequently, when the copy board is rested on the rails installed on the bent portions having remarkable positional errors, the prescribed positional relationship can not be established between the copy board and the illuminating apparatus even if the latter is located at the proper position. More specifically, even when the positions of the reflector and the lamp disposed in front of the reflector are correctly established relative to a reference position, the distances between the end portions of the illuminating lamp and a light collecting portion for collecting light rays emitted from the lamp upon energization thereof (which is located at a predetermined position on the moving path of the copy board) will become deviated from the proper one, which eventually means that the optical path extending from an elongated illuminating lamp through a known optical system including a lens to a light-sensitive surface of a drum becomes different at both end portions of the lamp.
The problems discussed above are inherently ascribable to the machining process for fabricating the machine frames provided with projections or bent portions. Assuming that the bent portions for securing the rails thereon are formed correctly along the respective ruled lines, an step is still indispensably required in the structure in which the reflector is secured at small size bent portions projecting from the frames, while the illuminating lamp is held by holders mounted on the frames in an electrically insulated manner, because different reference positions are adopted for mounting the reflector and the illuminating lamp.